Based on a notebook entry recorded at the time, de Forest asserted that, while working on the cascade amplifier, he had stumbled across the feedback principle on August 6, 1912, which was then used in the spring of 1913 to operate a low-powered transmitter for heterodyne reception of Federal Telegraph arc transmissions.
2.
Typical signal quality measures involving noise are signal-to-noise ratio ( SNR or " S " / " N " ), signal-to-quantization noise ratio ( SQNR ) in " E " b / " N " 0 in digital transmission, carrier to noise ratio ( CNR ) before the detector in carrier-modulated systems, and noise figure in cascaded amplifiers.
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